1. Field of the Invention
The invention relates to a process for recovering hard material particles which are present in a residue quantity, which is in a free-flowing or pourable form, of a hard metal which has a matrix consisting of a steel, of nickel or a of a nickel alloy, in which the hard material particles are embedded.
2. Description of Related Art
Hard metal materials of the type mentioned above are nowadays usually produced by powder metallurgy, melting metallurgy or spray compacting processes. Metal materials which have a lower melting point than the hard materials which are to be embedded in them in each case are normally used for the metal matrix.
Compositions of intermetallic phases, often metal carbides but also ceramic particles, are used as hard materials, which are typically based on a metallic bond. The hard materials used in practice correspondingly include, for example, carbides, such as TiC, WC, WC—W2C, NbC, SiC, B4C, Al4C3 or VC2, nitrides, such as AIN or TiN, borides, such as TiB2 or MgB2, and carbonitrides, such as Ti(C2N) or V(C,N).
Amongst other things, residues in the form of chips, residual pieces or defective pieces are formed, when machining hard metal materials of the previously mentioned type, which can be recycled. Returns, such as components which in practical use have become unfit due to wear and tear or a fault, also come under these recyclable residues. All these residues contain a high proportion of the respective hard material. Since manufacture normally requires a high input of energy and outlay of equipment, and hence the hard materials themselves represent a high value, from the point of view of saving resources and economy there is a requirement for the hard materials in question to be able to be recovered in a simple and cost-effective way.
DE 197 11 764 B4 describes various possibilities for recycling hard metal materials, in which hard material particles are bound in an aluminium matrix. All these possibilities are based on the concept of melting down the respective residues and subjecting them to treatment with an additive, such as a gas or a salt, or to a mechanical treatment, such as a separation by sedimentation, the effect of centrifugal forces or a cooled roller, which removes the molten metal from the melt bath, in order to separate the metal of the matrix material from the hard material particles.
In addition to the recycling processes based on melting the metal matrix of the hard metal, it is also known for example from the article “Selective removal of the cobalt binder in WC/Co based hard metal scraps by acetic acid leaching” by C. Edtmaier et al., Hydrometallurgy, Volume 76, Edition 1-2, January 2005, pages 63-71 that the cobalt proportion can be extracted from a tungsten carbide/cobalt hard metal material by means of acetic acid and oxygen added to the acid bath. Here, the WC particles bound in the cobalt remain as insoluble solid material.
One hard metal material, produced powder-metallurgically in the form of a metal-matrix composite (“MMC”) and successfully used in practice under the trademark “Ferro-Titanite”, contains up to 45% vol. titanium carbide (TiC) with a hardness of 3200 HV. With this material, the titanium carbide is embedded into a matrix consisting of steel, the properties of which are adapted to the respective intended use. Thus, ferro-titanite materials are available, as specified in detail in the “Ferro-Titanite® August 2003 collection of data sheets, in which the steel matrix is produced from a martensitic steel with very good tempering properties, from a highly corrosion-resistant steel, from an age-hardenable nickel-martensite steel with a high degree of toughness or from a non-magnetisable, highly corrosion-resistant steel with very good tempering properties. The contents of the particulate TiC hard material grains in the materials in question are in practice typically in the range of 30-35% wt.